"Of course she can, dummy," he said. "Now that you're in fourth grade, you need to know these things: Mommy is Santa."

Santa? Me? No, I'm just a mom.

A mom with a big problem.

How do you explain the unexplainable? Are you obligated, when your kids ask, to point out that you and Santa — how should I put this? — have never been photographed together?

My boys are straddling that fence between kid and teenager. They'll read Lord of the Rings, then Charlotte's Web; watch a Discovery Channel documentary, then flip to the Disney Channel. They play chess then with Play-Doh.

They think they're so grown.

Ryland, the fifth-grader, is quiet and logical.

Tucker is the opposite: Outspoken and artistic, he sees the world as he wants it to be.

"She is not Santa," Tucker spat at his brother. He turned to me, defiant and desperate. "Are you, Mom?"

My husband, Dan, was still at the stove, slopping batter like nothing had happened. Ryland, looking smug, was drizzling more syrup onto his stack.

Tucker's lower lip started quivering.

"Well, honey," I said, "what do you think?"

"A lot of kids in my class say there's no Santa," Tucker said, jutting his chin. "But I always tell them to shut up. Of course there is."

Silence from me and Dan. Snickers from Ryland.

"Anyways, you can't be Santa," Tucker said.

"If you were the one who really bought us all those presents, you'd put your name on them 'cause you'd want us to know how much money you spent."

For a while, Tucker picked at his pancake. We talked about homework they had to do that day. "Maybe when you finish," I said, "we can take a bike ride."

Tucker snapped his head toward me. "About our bikes," he said, as if unearthing a key clue, "you said you couldn't afford new bikes that year. But we got them for Christmas. So that had to be Santa, right?"

Dan stared at me. The kid was homing in.

"Remember," Dan said gently, "just before Christmas, Mom sold her car."

Finally, he looked up. "You have to tell me," he said, narrowing his blue eyes. "Are you Santa?"

If only I'd done the dishes ...

Ryland couldn't be right. He just couldn't. There were so many signs of Santa — heck, Tucker had sat on the old dude's lap.

"An imposter," Ryland said. "Didn't you notice? That guy at the mall had stick-on eyebrows."

"What about the reindeer?" Tucker tried again. We always spread dry oatmeal around the fireplace so the reindeer have a snack too.

"Remember?" Tucker said. "Last year we even found a pile of reindeer poo."

"That," I said, "was a gift from your dog."

The interrogation lasted all day.

"If you're Santa, why did you make up that guy in the red suit?"

If it isn't true, it's a lie.

"So why did you lie to me? Didn't you tell me never to tell a lie?"

I tried to explain: I didn't make up Santa. He's everywhere. He's the spirit of Christmas, of giving and caring someone who knows whether you're naughty or nice, who rewards you when you're good, who watches over you.

"Isn't that Jesus?" Tucker asked. "And God?"

He figured those guys already are part of Christmas. "So why do you need Santa, too?"

I was putting the boys to bed that night when Tucker called down from the top bunk.

"Hey, Mom," he said, "remember last Christmas Eve, when Dad and Ryland were asleep, and me and you heard that thump on the roof and we thought maybe that was Santa?"

"Yep. I remember."

"What was that, Mom?"

I pulled up his comforter, kissed his cheek. Turned off the light. "I don't know," I answered honestly. "It could have been anything."